Cemented hard metal carbide material is advantageously used in many products because of its inherent hardness and wear resistant properties. Such cemented hard metal carbide products have found a wide variety of uses, but probably the widest known use is in cutting inserts used in metal cutting operations.
When cutting inserts are made of carbide material and used to remove metal, the metal chip being removed from the workpiece usually slides over the substrate carbide material thereby producing a frictional wear on the insert which, if it continues long enough, will brecek down the cutting edge of the insert and cause a cratering effect inward of the cutting edge on the cutting insert.
Preferably, in this application, reference will be made to cutting inserts using a triple coating applied according to the present invention. However, it is also known that carbide punches used in forming metal materials may also be coated according to the process of the present invention in order to obtain advantageous results.
Coatings for cutting inserts made from cemented carbide materials are known, and the advantages of these coatings are also widely known. For instance, it is known that superior results can be achieved by coating the carbide cutting insert with a first coating of titanium carbide and then providing a top coating of titanium nitride over the first layer of titanium carbide. The advantage found in applying titanium carbide is that the coating layer has an extreme hardness to it, yet, the titanium carbide coating does not have as good a wear resistance as that of titanium nitride.
Therefore, by coating the insert with a first coating of titanium carbide, a superior hardness is achieved, and by putting the coating of titanium nitride above the coating of titanium carbide, a superior wear resistance is achieved. The titanium nitride also has superior advantages in that the coefficient of sliding friction between the titanium nitride coating and the metal chip being removed from the workpiece is less than when the titanium carbide coating or the bare substrate material would have when contacting the metal chip.
It is also known to put a coating of metal nitride by itself on the metal carbide substrate in order to take advantage of the more wear resistant properties of the metal nitride. The metal nitride, however, does not have as good a hardness as that of the metal carbide and, in addition, it has been found that, when the metal nitride coating is used by itself, it tends to spall and flake off and, therefore, does not offer the protection desired for the metal carbide substrate material.
One of the problems that is associated with any coating on a metal carbide substrate is that there is a heat build-up on the coating due to the metal chips being removed from the workpiece, and coatings such as metal nitride over a metal carbide coating, as mentioned above, begin to wear or flake off after a certain period of use.
It is also known to use as a coating on such carbide substrates a metal carbo-nitride coating by itself in order to take advantage of the superior properties of each of the metal carbide or metal nitride compounds.
It is an object of the present invention to apply three layers of coatings on the carbide substrate in such a manner that superior bonding is achieved between the first coating and the substrate material and, also, to advantageously use the superior properties of the metal carbide in conjunction with the metal nitride.
It is a further object of the present invention to provide a carbide substrate which is also resistant to any corrosive atmosphere in which it may operate.
It is a further object of the present invention to provide a longer lasting coating which will prevent the carbide substrate material from wearing away.